Exhaust gas apparatus and method for the regeneration of a nox trap and a particle filter

ABSTRACT

Exhaust gas apparatus for the cleaning of exhaust gas where the exhaust gas apparatus comprises an exhaust conduit section which is formed with at least two separate flow paths. Each flow path is provided with a particle filter for the removal of particulate matter from the exhaust gas, an NOx trap for the removal of NOx from the exhaust gas. The exhaust gas apparatus further comprises at least one cold flame vaporizer in which fuel is partially oxidized in preheated air to form a cold flame gas where the cold flame vaporizer is arranged in fluid communication with each of the flow paths in the exhaust conduit section such that the cold flame gas can flow through the particle filter and the NOx trap, and valve means for controlling the flow of cold flame gas from the cold flame vaporizer to each flow path in the exhaust conduit section. Thereby, both the particle filter and the NOx trap in at least one of the flow paths can be regenerated in a single operation. There is also provided a method for regenerating cleaning means for exhaust gas where the cleaning means comprises an NOx trap and possibly a particle filter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.12/675,400, filed Feb. 26, 2010, which was a National Stage applicationof PCT/NO2008/000310 filed Sep. 1, 2008, and claims the benefit of U.S.Provisional application 60/968,899 filed Aug. 30, 2007.

BACKGROUND

The present invention relates to apparatus for regenerating a NOx trapand the regeneration of a particle filter and a NOx trap in a singleoperation. The invention is also related to a method for theregeneration of a NOx trap and a method for regenerating a particlefilter and a NOx trap in a single operation. The invention furtherrelates to the use of the apparatus and the methods with a compressionignition engine, i.e. what is often called a diesel engine.

The cold flame is a phenomenon which has so far not received to muchattention. In a cold flame the fuel is partially oxidized in preheatedair and the temperature is kept constant at about 450° C., and it isindependent of air/fuel ratio and residence time. In the cold flameprocess, only 2-20% of the calorific value of the fuel is released, andthis heat is used to evaporate the fuel, giving a homogenous gaseousfuel. During developmental work, it has been observed that the gas wasable to remove carbon deposits from the reactor walls. The reason forthis has not been established yet, but is thought to be due to freeradicals that are present in the cold flame gas, i.e. the partiallyoxidized, gaseous fuel.

A more complete description of the cold flame gas phenomenon can befound in the American patent, U.S. Pat. No. 6,793,693.

Exhaust from compression ignition engines (often imprecisely calleddiesel engines), which operate on excess air, contains mainlyparticulates, NOx and incomplete combustion products (HC and CO).Particulates can be removed using a filter downstream from the engine.After a while, the filter will be blocked and need to be regenerated.This is done by increasing the temperature in the exhaust gas to above600° C. under oxidizing conditions and thereby burning away the carbondeposits. In order to allow for continuous operation, it is common tohave two filters in parallel and a valve which sends the majority of theexhaust to one of the filters while the other is being regenerated.

Incomplete combustion products (HC and CO) can be removed by anoxidation catalyst.

NOx, on the other hand, can only be removed catalytically if the exhaustgas is slightly reducing (as in an Otto engine). This is not normallythe case in a compression ignition engine. Since the regenerating of theparticle requires an oxidizing environment while the regenerating of theNOx trap requires a slightly reducing environment, there has not beenavailable a method for regenerating the particle filter and the NOx trapin a single operation.

One way to reduce NOx emissions in a diesel engine is to recirculatesome of the exhaust back into the engine (EGR).

While the above method reduces the NOx formation, it is also possible toremove NOx by inserting an NOx absorbent, as described in several patentdocuments, for instance U.S. Pat. No. 5,974,791. An NOx absorbent can bemade from barium carbonate. During absorption, the absorbent isconverted to barium nitrate and releases CO₂ at the same time. When theabsorbent is saturated, it can be regenerated using CO in that thebarium nitrate is converted back to barium carbonate and release N₂ gas.

For a complete treatment of the exhaust gas, a particle filter+an NOxabsorber (NOx trap)+an oxidation catalyst is used. The problem is, asalready mentioned, that the particle filter has to be regenerated underhigh temperature (600° C.) in an oxidizing environment while the NOxabsorber is regenerated at lower temperatures in a reducing environment(500° C. with CO gas). This means that two process operations are neededin order to clean both the particle filter and the NOx trap, asdescribed in the American patent U.S. Pat. No. 6,955,042.

BRIEF SUMMARY OF THE INVENTION

There is therefore an objective of the present invention to find a newway to regenerate an NOx trap.

A further objective of the present invention has been to find a way toregenerate the particle filter and the NOx trap in a single operation.

These objectives are achieved by the present invention as defined in theindependent claims. Further embodiments of the invention is defined inthe dependent claims.

There is provided an exhaust gas cleaning apparatus for the cleaning ofexhaust gas flowing in an exhaust gas conduit. The exhaust cleaningapparatus comprises at least one NOx trap arranged in the exhaust gasconduit such that the NOx trap at least partially removes NOx from theexhaust gas flowing through the exhaust gas conduit. The exhaust gascleaning apparatus further comprises a cold flame vaporizer wherein fuelis partially oxidized in preheated air to form a cold flame gas. Thecold flame vaporizer is arranged in fluid communication with the exhaustgas conduit such that the cold flame gas can flow through the NOx trapin the exhaust gas conduit, thereby regenerating the NOx trap.

The cold flame vaporizer is a standard cold flame vaporizer in which thefuel can be partially oxidized in preheated air. In the cold flamevaporizer air and fuel is mixed in a proportion of typically 0.3-1.0(1.0 is stoichiometric air/fuel ratio), but only a small fraction of theair is used in the cold flame reaction.

The exhaust gas conduit may be a pipe or similar of any cross sectionalshape, or the exhaust gas conduit may be formed as internal conduits ina larger body.

The means for preheating the air may be a heat exchanger in which theheat of the exhaust gas warms up the air. It would also be possible touse other means for preheating the, for instance electrical heatingmeans.

The cold flame vaporizer may be arranged outside the exhaust gas conduitand, if necessary, connected to the exhaust gas conduit with fluidlines. If the cold flame vaporizer is mounted to the exhaust gasconduit, then there may only be necessary to provide openings into theexhaust gas conduit, while if the cold flame vaporizer is arrangedseparate from the exhaust gas conduit, fluid lines will be providedconnecting the cold flame vaporizer and the exhaust gas conduit.

In an embodiment of the invention, the cold flame vaporizer can also bearranged inside the exhaust gas conduit. In that case, there is no needfor fluid lines as the cold flame vaporizer may just release the coldflame gas into the exhaust gas conduit through openings including saidvalve means.

The exhaust gas cleaning apparatus further comprises valve meanscontrolling the flow of cold flame gas from the cold flame vaporizerinto the exhaust gas conduit.

The exhaust gas cleaning apparatus is further provided with one or morevalve means which controls the flow of exhaust gas through the exhaustgas conduit. When regenerating the NOx trap in the exhaust gas conduit,the flow of exhaust gas can therefore at least partially be shut off.

These valve means may be controlled such that the NOx trap isregenerated, for instance, at specific time intervals, or when thepressure drop across NOx trap reaches a predetermined level indicatingthat the NOx trap needs to be regenerated.

Furthermore, the exhaust gas cleaning apparatus comprises a fuel supplywhich is arranged in fluid communication with the cold flame vaporizer.The exhaust gas cleaning apparatus also comprises an air supply andmeans for preheating the air, the air supply being in fluidcommunication with the cold flame vaporizer. In order to control theflow of fuel and preheated air into the cold flame vaporizer, theexhaust gas apparatus comprises one or more valve means controlling theflow of fuel and preheated air to said cold flame vaporizer.

There is also provided an exhaust gas apparatus for the cleaning ofexhaust gas, the exhaust gas apparatus comprising an exhaust conduitsection which is formed with at least two separate flow paths. Each flowpath is provided with a particle filter for the removal of particulatematter from the exhaust gas and an NOx trap for the removal of NOx fromthe exhaust gas. The exhaust gas apparatus further comprises at leastone cold flame vaporizer in which fuel is partially oxidized inpreheated air to form a cold flame gas. The cold flame vaporizer isarranged in fluid communication with each of the flow paths in theexhaust conduit section such that the cold flame gas can flow throughthe particle filter and the NOx trap. There is further provided valvemeans for controlling the flow of cold flame gas from the cold flamevaporizer to each flow path in the exhaust conduit section, whereby boththe particle filter and the NOx trap in at least one of the flow pathscan be regenerated in a single operation.

The cold flame vaporizer is a standard cold flame vaporizer in which thefuel can be partially oxidized in preheated air. In the cold flamevaporizer air and fuel is mixed in a proportion of typically 0.3-1.0(1.0 is stoichiometric air/fuel ratio), but only a small fraction of theair is used in the cold flame reaction.

The exhaust gas conduit may be a pipe or similar of any cross sectionalshape, or the exhaust gas conduit may be formed as internal conduits ina larger body.

The means for preheating the air may be a heat exchanger in which theheat of the exhaust gas warms up the air. It would also be possible touse other means for preheating the air, for instance electrical heatingmeans.

The flow paths may be formed by providing the exhaust gas returnconduit, at least along a part of its length, with one or morepartitions such that two or more separate flow paths for the exhaust gasare formed in the exhaust conduit section. These partitions may be oneor more plates dividing the exhaust gas return conduit in two or moreflow paths. Alternatively, the flow paths may be formed by providing theexhaust gas return conduit with at least two separate conduits throughwhich the exhaust gas can flow.

The cold flame vaporizer may be arranged outside the exhaust conduitsection and, if necessary, connected to the exhaust conduit section withfluid lines. If the cold flame vaporizer is mounted to the exhaustconduit section, then there may only be necessary to provide openingsinto the exhaust conduit section, while if the cold flame vaporizer isarranged separate from the exhaust conduit section, fluid lines will beprovided connecting the cold flame vaporizer and the exhaust conduitsection.

In an embodiment of the invention, the at least one cold flame vaporizercan also be arranged inside the exhaust conduit section. In that case,there is no need for fluid lines as the cold flame vaporizer may justrelease the cold flame gas into the exhaust gas conduit through openingsincluding said valve means.

The exhaust gas apparatus is preferably provided with one or more valvemeans which controls the flow of exhaust gas through the flow paths ofthe exhaust conduit section. The valve means may close off one or moreflow paths for the flow of exhaust gas. The exhaust gas apparatus ispreferably also provided with one or more valve means controlling theflow of cold flame gas from the at least one cold flame vaporizer to theflow paths of exhaust conduit section and the particle filters and NOxtraps in the flow paths. These valve means may be controlled such thatthe particle filters and NOx traps are regenerated, for instance, atspecific time intervals, or when the pressure drop across a particlefilter and/or NOx trap reaches a predetermined level indicating that theparticle filter and the NOx trap needs to be regenerated.

The exhaust gas apparatus further comprises a fuel supply which isarranged in fluid communication with the at least one cold flamevaporizer. Preferably, there is also provided valve means controllingthe flow of fuel to the at least one cold flame vaporizer.

The exhaust gas apparatus also comprises an air supply and, as mentionedabove, means for preheating the air, the air supply being arranged influid communication with the at least one cold flame vaporizer.Preferably, there is also provided valve means controlling the flow ofpreheated air to the at least one cold flame vaporizer.

In each flow path, the NOx trap is preferably arranged downstream of theparticle filter so that particulate matter in the exhaust gas can beremoved before reaching the NOx trap.

Preferably, the exhaust gas apparatus also comprises an oxidationcatalyst arranged downstream of the particle filter and the NOx trap.

There is also provided a method for regenerating an NOx trap whichremoves NOx from exhaust gas flowing in an exhaust gas conduit, the NOxtrap being provided in the exhaust gas conduit, the method comprisingthe following steps:

-   -   providing a cold flame gas,    -   letting the cold flame gas flow through the NOx trap, thereby        regenerating the NOx trap.

There is also provided a method for regenerating cleaning means forexhaust gas flowing in an exhaust gas conduit where the cleaning meanscomprises a particle filter for the removal of particulate matter fromthe exhaust gas and an NOx trap for the removal of NOx from the exhaustgas wherein the particle filter and the NOx trap being arranged in theexhaust gas conduit. The method comprises the following steps:

-   -   providing a cold flame gas,    -   letting the cold flame gas flow through the particle filter and        the NOx trap, thereby regenerating both the particle filter and        the NOx trap in a single operation.

Again, the cold flame gas may be provided by partially oxidizing fuel inpreheated air in a cold flame vaporizer which is arranged in fluidcommunication with the exhaust conduit. In the cold flame vaporizer airand fuel is mixed in a proportion of typically 0.3-1.0, but only a smallfraction of the air is used in the cold flame reaction.

In order to remove particulate matter from the exhaust gas before theexhaust gas passes through the NOx trap, the method also comprises thestep of arranging the NOx trap downstream of the particle filter.

The method also comprises the step of providing one or more valve meansfor controlling the flow of cold flame gas from the cold flame vaporizerinto the exhaust gas conduit.

The method also comprises the step of providing a fuel supply arrangedin fluid communication with the cold flame vaporizer, and an air supplyand heating means for the preheating of the air, the air supply beingarranged in fluid communication with the cold flame vaporizer.Furthermore, the method comprises the step of providing valve means forcontrolling the flow of fuel and preheated air to the cold flamevaporizer.

There is also provided a method for regenerating cleaning means forexhaust gas flowing through an exhaust conduit section of an exhaust gasconduit, the exhaust conduit section being formed with at least two flowpaths for the exhaust gas. The cleaning means are provided in each ofthe flow paths and comprises

-   -   a particle filter for the removal of particulate matter from the        exhaust gas,    -   an NOx trap for the removal of NOx from the exhaust gas        The method comprises the following steps:    -   providing a cold flame gas,    -   letting the cold flame gas flow through the particle filter and        the NOx trap in at least one of the flow paths of the exhaust        conduit section.        The particle filter and the NOx trap in the at least one flow        path are thereby both, in one operation, regenerated.

As mentioned several times, the cold flame gas may be provided bypartially oxidizing fuel in preheated air in at least one cold flamevaporizer which is arranged in fluid communication with all the flowpaths of the exhaust conduit section. In the cold flame vaporizer airand fuel is mixed in a proportion of 0.3-1.0 (again 1.0 isstoichiometric air/fuel ratio), but only a small fraction of the air isused in the cold flame reaction.

The method also comprises the step of providing one or more valve meansfor separately controlling the flow of cold flame gas from the coldflame vaporizer into each flow path of the exhaust gas conduit.

Furthermore, the method also comprises the step of providing a fuelsupply arranged in fluid communication with the cold flame vaporizer,and an air supply and heating means for the preheating of the air, theair supply being arranged in fluid communication with the cold flamevaporizer.

The method also comprises the step of providing one or more valve meansfor controlling the flow of fuel and preheated air to the cold flamevaporizer.

The method also comprises the step of arranging, in each flow path inthe exhaust conduit section, the NOx trap downstream of the respectiveparticle filter.

The method also comprises the step of arranging an oxidation catalyst inthe exhaust conduit section downstream of the particle filter and theNOx trap.

There is also provided a use of the exhaust gas cleaning apparatus wherethe NOx trap is arranged in the exhaust conduit of a compressionignition engine.

There is also provided a use of the exhaust gas apparatus wherein theexhaust conduit section forms part of the exhaust gas conduit of acompression ignition engine.

There is also provided a use of the method for regenerating an NOx trapwherein the NOx trap is arranged in the exhaust conduit of a compressionignition engine.

There is also provided a use of the methods for regenerating cleaningmeans for exhaust gas, the cleaning means comprising a particle filterand an NOx trap, with a compression ignition engine.

Above, only a cold flame gas produced by a cold flame vaporizer has beenmentioned. A cold flame is one method to achieve a partially oxidizedfuel gas among a number of other partially oxidized fuel gases with thesame properties. The present invention should therefore not be seen aslimited to only a cold flame gas, but should include other partiallyoxidized fuel gases with the same or similar properties as the coldflame gas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, an embodiment of the invention is disclosed in detailwith reference to the enclosed figures, where

FIG. 1 illustrates an embodiment of the invention where a NOx trap isarranged in an exhaust conduit.

FIG. 2 a illustrates an embodiment of the invention where a particlefilter and a NOx trap is arranged in a section of an exhaust conduitwhich is.

FIG. 2 b is an illustration of the section A-A through the particlefilter in FIG. 2 a.

FIG. 2 c is an illustration of the section B-B through the NOx trap inFIG. 2 a.

FIG. 3 a illustrates a similar embodiment of the invention where aparticle filter and a NOx trap is arranged in a section of an exhaustconduit.

FIG. 3 b an illustration of the section A-A through the particle filterin FIG. 3 a.

FIG. 3 c an illustration of the section B-B through the particle filterin FIG. 3 a.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a first embodiment of the invention. An exhaust gasflows in an exhaust gas conduit 14 with valve means 18 controlling theflow of exhaust gas through a NOx trap 30.

There is also provided a cold flame vaporizer 11 with a fuel supply 12,which may be diesel or heavy fuel oil, and an air supply 13. The airsupply may be provided with an air intake 15 including an air filter(not shown). Valve means 16, 19 controls the flow of air through fluidline 25 and flow of fuel through fluid line 26 to the cold flamevaporizer 11 respectively.

When the NOx trap needs to be regenerated, valve means 18 is preferablyclosed and valve means 17 is opened such that cold flame gas can flowthrough the NOx trap, thereby regenerating it.

In FIG. 2 a-2 c there is shown a second embodiment of the invention.Exhaust gas, indicated by arrow 20 on the figure, flows in exhaust gasconduit 14 and through an exhaust conduit section 10 comprising at leasta particle filter 30 and a NOx trap 40. Further downstream there isprovided an oxidation catalyst 50. The oxidation catalyst could also beplaced together with the particle filter 30 and the NOx trap 40.

The exhaust conduit section 10 is formed with two separate flow paths ascan easily be seen on FIGS. 2 b and 2 c, which illustrate sectionsthrough the particle filter 30 and the NOx trap 40 respectively. The twoflow paths are formed by a partition 25 dividing the exhaust conduitsection 10 in two parts in the longitudinal direction. In each flow paththere is provided a particle filter 30 and a NOx trap 40. There is alsoprovided means, like valve means, to control the flow of exhaust gas andcold flame gas through the exhaust conduit section 10.

There is also provided a cold flame vaporizer 11 with a fuel supply 12and an air supply 13. There is no difference from the first embodimentof the invention shown in FIG. 1, so it will not be described anyfurther here.

When the particle filters 30 and the NOx traps 40, arranged in the fluidpaths 41 and 42 in the exhaust conduit section 10, are to be regeneratedusing the cold flame gas from the cold flame vaporizer 11, one of theflow paths 41, 42 is closed for the flow of exhaust 20 while the otherflow path is kept open for the flow of exhaust gas. Valve means 17 areopened and cold flame gas flows through the flow path 41, 42 which hasbeen for the flow of exhaust gas. The particle filter 30 and the NOxtrap 40 in that flow path are thereby regenerated in one operation whileexhaust gas is allowed to flow through the other flow path. There istherefore not necessary to stop the engine from which the exhaust gasoriginates.

When the particle filter and the NOx trap in one flow path 41, 42 havebeen regenerated, the valve means switches positions so that the exhaustgas now flows through the flow path 41, 42 containing the regeneratedparticle filter and NOx trap, while the cold flame gas is directedthrough the flow path 41, 42 in which the particle filter 30 and NOxtrap 40 is not yet regenerated. The regeneration of the particle filter30 and the NOx trap 40 can thereby be carried out in one operationwithout having to stop the engine.

In this embodiment of the invention, the exhaust conduit section 10 isprovided with only two flow paths 41, 42. It is however, possible toprovide any number of flow paths for the exhaust gas through the exhaustconduit section 10

In FIG. 3 a-3 c a very similar embodiment of the invention to theembodiment on FIG. 2 a-2 c, is shown. Again the cold flame vaporizer 11with its fuel supply 12 and air supply 13 is identical to what hasalready been described and will not be repeated.

The embodiment of the invention shown on FIG. 3 a-3 c is also providedwith two flow paths 34, 35 through which the exhaust gas may flow, butare now in the form of two separate exhaust gas conduits. There is alsoprovided fluid lines so that cold flame gas from the cold flamevaporizer 11 can flow through the two flow paths 34, 35.

Flow paths 34, 35 are provided with valve means 32, 33 which control theflow of exhaust gas through the two flow paths. Valve means 17 controlthe flow of cold flame gas to through the two flow paths 34, 35.

Both flow paths are provided with a exhaust conduit section 10comprising at least a particle filter 30 and a NOx trap 40. On FIG. 3 ait is also shown that the exhaust conduit section 10 comprises anoxidation catalyst, but this is optional as mentioned above.

As before, when the particle filters 30 and the NOx traps 40 need to beregenerated, one of the flow paths 32, 33 is closed for the flow ofexhaust gas by valve means 32, 33 and the one of valve means 17 openssuch that cold flame gas from the cold flame vaporizer 11 is directed toand flows through the exhaust conduit section 10 which has been closedfor the flow of exhaust gas. The particle filter 30 and the NOx trap inone of the exhaust conduit sections 34, 35 are regenerated by the coldflame gas in one operation.

Later the direction of flow of exhaust gas and cold flame gas throughthe two exhaust conduit sections will change so that the particle filter30 and the NOx trap 40 in the other exhaust conduit section 10 are alsoregenerated by the cold flame gas.

FIGS. 3 b and 3 c are sections through the particle filters 30 and theNOx trap 40 respectively. As can be seen on the figure, the filterscover substantially the whole cross section as opposed to the embodimentshown in FIG. 2 a-2 c.

Again, the embodiment shown on FIG. 3 a-3 c are provided with two flowpaths 34, 35, but it would be possible to provide as many flow paths asis necessary for any given purpose.

1. Exhaust gas apparatus for the cleaning of exhaust gas, the exhaustgas apparatus comprising an exhaust conduit section which is formed withat least two separate flow paths, each flow path being provided with aparticle filter for the removal of particulate matter from the exhaustgas, an NOx trap for the removal of NOx from the exhaust gas, whereinthe exhaust gas apparatus further comprises at least one cold flamevaporizer in which fuel is partially oxidized in preheated air by a coldflame such that 2-20% of the calorific value of the fuel is released,whereby a cold flame gas is formed, the cold flame vaporizer is arrangedin fluid communication with each of the flow paths in the exhaustconduit section such that the cold flame gas can flow through theparticle filter and the NOx trap, and one or more valves for controllingthe flow of cold flame gas from the cold flame vaporizer to each flowpath in the exhaust conduit section, whereby both the particle filterand the NOx trap in at least one of the flow paths can be regenerated ina single operation.
 2. Exhaust gas apparatus according to claim 1,wherein the flow paths are formed by providing the exhaust conduitsection as one conduit with one or more partitions such that two or moreseparate flow paths for the exhaust gas are formed in the exhaustconduit section.
 3. Exhaust gas apparatus according to claim 1, whereinthe flow paths are formed by providing the exhaust conduit section withat least two separate conduits through which the exhaust gas can flow.4. Exhaust gas apparatus according to claim 1, wherein the at least onecold flame vaporizer is arranged outside the flow paths and that thecold flame vaporizer, is connected to each of the flow paths of theexhaust conduit section by fluid lines or conduits.
 5. Exhaust gasapparatus according to claim 1, wherein the at least one cold flamevaporizer is arranged within the exhaust conduit section.
 6. Exhaust gasapparatus according to claim 1, wherein the exhaust gas apparatuscomprises one or more valve controlling the flow of exhaust gas througheach of the flow paths of the exhaust conduit section.
 7. Exhaust gasapparatus according to claim 1, wherein the exhaust gas apparatuscomprises a fuel supply which is arranged in fluid communication withthe cold flame vaporizer.
 8. Exhaust gas apparatus according claim 1,wherein the exhaust gas apparatus comprises an air supply and a heatexchanger or electrical heater for preheating the air, the air supplybeing arranged in fluid communication with the cold flame vaporizer. 9.Exhaust gas apparatus according to claim 7 or 8, wherein the exhaust gasapparatus comprises one or more valve controlling the flow of fuel andpreheated air to the cold flame vaporizer.
 10. Exhaust gas apparatusaccording to claim 1, wherein, in each flow path, the NOx trap isarranged downstream of the particle filter.
 11. Exhaust gas apparatusaccording to claim 1, wherein the exhaust gas apparatus comprises anoxidation catalyst arranged downstream of the particle filter and theNOx trap.
 12. Method for regenerating cleaning means for exhaust gasflowing through an exhaust conduit section of an exhaust gas conduit,the exhaust conduit section being formed with at least two flow pathsfor the exhaust gas, the cleaning means being provided in each of theflow paths and comprising a particle filter for the removal ofparticulate matter from the exhaust gas, an NOx trap for the removal ofNOx from the exhaust gas, wherein the method comprises the followingsteps: providing a cold flame gas by partially oxidizing a fuel inpreheated air in a cold flame such that 2-20% of the calorific value ofthe fuel is released, the released heat being used to evaporate the fuelthereby forming the cold flame gas, letting the cold flame gas flowthrough the particle filter and the NOx trap in at least one of the flowpaths of the exhaust conduit section, thereby, in one operation,regenerating both the particle filter and the NOx trap in said at leastone flow path.
 13. Method according to claim 12, wherein the methodfurther comprises the step of providing one or more valves forseparately controlling the flow of cold flame gas from the cold flamevaporizer into each flow path of the exhaust gas conduit.
 14. Methodaccording to claim 12, wherein the method further comprises the step ofproviding a fuel supply arranged in fluid communication with the coldflame vaporizer, and an air supply and a heat exchanger or electricalheater for the preheating of the air, the air supply being arranged influid communication with the cold flame vaporizer.
 15. Method accordingto claim 14, wherein the method further comprises the step of providingone or more valves for controlling the flow of fuel and preheated air tothe cold flame vaporizer.
 16. Method according to claim 12, wherein themethod further comprises the step of arranging, in each flow path in theexhaust conduit section, the NOx trap downstream of the respectiveparticle filter.
 17. Method according to claim 12, wherein the methodfurther comprises the step of arranging an oxidation catalyst in theexhaust conduit section downstream of the particle filter and the NOxtrap.
 18. Method for regeneration of a NOx trap wherein a cold flame gasis flowed through the NOx trap such that the NOx trap is regenerated.19. Method for regeneration of a particle filter and a NOx trap in asingle operation wherein a cold flame gas, which is formed by partiallyoxidizing a fuel in preheated air in a cold flame such that 2-20% of thecalorific value of the fuel is released, the released heat being used toevaporate the fuel, thereby forming the cold flame gas, is flowedthrough the particle filter and the NOx trap such that the particlefilter and the NOx trap are regenerated.